3" exhaust on a non forced induction truck?

[jamisobe]

Originally Posted by Nay

Any reason you couldn't tuck the muffler up horizontal where the stock sub gas tank would go once your spare is gone and then vent over the frame rail out the side if you have a tube bumper like me? That would take the muffler out of it's normal low hanging contact point entirely, and the whole assembly would be completely out of the way.

The only thing I can think of that could be an issue is loss of scavenging. Tuned exhaust heat and pulses can help to pull the spent gases out of the combustion chambers. When the exhaust starts to cool down, before its done with the tricks it has to do to get out, more back pressure is created and you can loose scavenging advantages.

Some tricks include mufflers, cats, bends, welds, sharp angled bends, crimped bends, and the biggest and best trick of them all, the turbo. Of course, the turbo eliminates scavenging, but who cares? Though back pressure can increase resistance to compressor output.

Obviously there is a compromise in exhaust design between ergonomics and performance. Question is how far can you tilt the design to performance and still be ergonomic?

[Nay]

Thanks for the input, I'll consult with the shop when I get to that point.

[jamisobe]

I wouldn't assume that the Midas guys are experts. I once had a leak in my 3" system at the hanger where the tube went under the frame (it also had a crunch and a little surface rust) and the guy at the shop told me I needed to scrap the whole system and install a new stock system. was my response. The guy wasn't happy and I left horrified - and still leaking.

There is a good technical write up on exhaust science out on the Super Chevy web site. Auto Exhaust Science
No definitive answers, but a discussion of variables that would be altered by changing the length of tubing before the muffler.

"When we dealt with collector length it was emphasized that it was, in most cases, more critical than the primary pipe lengths. Adding a muffler (even one with zero backpressure) to a system with already optimized lengths can alter the pressure wave response such that the tuning is now out of phase with what is required and as a result, power drops. The trick here is to install mufflers such that they don't alter the tuned lengths of the system."

[LC80Ducati996]

Originally Posted by landtank

It's coming, cast manifolds don't happen over night.

Actually it could. for $682

Turbonetics Exhaust Manifold - Sport Compact Warehouse - Import Performance Specialist

Ohhh $606

Exh. Manifold, Toyota Landcruiser - Turbochargers.com

But overnight shiping would be spendy,

[LC80Ducati996]

Originally Posted by jamisobe

There is a good technical write up on exhaust science out on the Super Chevy web site. Auto Exhaust Science
No definitive answers, but a discussion of variables that would be altered by changing the length of tubing before the muffler.

One huge difference, losses or gains on an engine with a much milder camshaft such as a stock 1FZ-FE are not as great as on a cammed up muscle car motor with a big overlap on the cams.

Also even if you turbo it the stock cam might likely be the best available since overlap with turbo exhaust manifold pressure is bad where as a supercharged rig could use a bit more exhaust duration..

For stock I say 3" cat back is fine so long as the transition from stock to 3" does not occur in one giant step nor too close to the engine. Maintaining exhaust velocity is a biggest issue on our rigs. If one had tuned equal length headers and a big cam then pulse tuning of the whole system would be a bigger deal.. For us run with the general rule of thumb that exhaust diameter should increase as the exhaust cools.

[jamisobe]

Originally Posted by LC80Ducati996

One huge difference, losses or gains on an engine with a much milder camshaft such as a stock 1FZ-FE are not as great as on a cammed up muscle car motor with a big overlap on the cams.

Also even if you turbo it the stock cam might likely be the best available since overlap with turbo exhaust manifold pressure is bad where as a supercharged rig could use a bit more exhaust duration..

For stock I say 3" cat back is fine so long as the transition from stock to 3" does not occur in one giant step nor too close to the engine. Maintaining exhaust velocity is a biggest issue on our rigs. If one had tuned equal length headers and a big cam then pulse tuning of the whole system would be a bigger deal.. For us run with the general rule of thumb that exhaust diameter should increase as the exhaust cools.

Scavenging is definitely a bigger deal on engines with camshafts that have increased overlap. But nearly all modern 4-stroke engines have overlap in the camshafts as a standard design feature. Heads that flow better also have a more pronounced benefit to gain from scavenging. The 1FZFE does have 4 valves per cylinder which does assist in flow. Headers, a high flow collector, a high flow MAF, or a high flow cat will also assist in scavenging depending on the length of the secondary pipe and the tuning of the pulse. For race engines scavenging plays a huge role to intake fuel/air (more than down stroke). Though the gains to be had from scavenging may not be as large as those from a lumpy race cam there still are significant gains to be had in the 1FZFE if the system flows well.

There is such thing as having exhaust that is too big. The link I reference here gives a general rule of thumb for exhaust tube diameter vs engine displacement.

MagnaFlow Performance Exhaust - FQA, Frequently Asked Questions

I have not spent any time on a track or dyno experimenting with the secondary length for maximum pulse tuning. I don't know how close I am to having the ideal scavenging effect. I know that my exhaust flows better than stock and I don't have the same power complaints as many. If I did not have an exhaust modified for flow I would not be running 3" pipe (probably 2.5").

The link below also talks in detail about secondary length and how tuning the end of the secondary effects performance significantly. For lower end torque and street use I have read an approximate length of 50 inches used. For high RPM, strip use 10-12 inches. Also, I have read that the tri-Y header systems do also slightly favor lower end torque (this is what Downey is selling although it is up to the buyer to arrange for the final Y collector).

I have never read or even heard of anyone recommend a neck up, after the secondary/collector for performance gain. Common sense tells me this would introduce turbulence and encourage cooling before exit which would create back pressure.


Auto Exhaust Science

[LC80Ducati996]

You dont ever want to neck a pipe you are right they kill flow. A long tapered transition is preffered. There is even an optimum angle that it should expand at. It is very small angle. A smooth cone at this angle has more flow than a smooth straight pipe.

http://www.tantrumwerks.com/html/Spl...t%20theory.pdf


Anyway what I am getting at is going from stock or near stock diameter from the collectors to the cats and using a long 7-12 degree conical transition to go up to the 3" will likely perform better than going to a 3" collector at the OEM Y or going with larger tri ys.. You will have more velocity where it does the most good and more flow farther down where gases have cooled off after the cat(s).

I really dont want custom headers but a turbonetics manifold..

I did some research compared to a turbo diesel convo.. I can turbo the 1FZ, add a sub tank, get a econo box honda for heavy rain days (ride cycle nice ones) and have money to spare..

[jamisobe]

Originally Posted by LC80Ducati996

You dont ever want to neck a pipe you are right they kill flow. A long tapered transition is preffered. There is even an optimum angle that it should expand at. It is very small angle. A smooth cone at this angle has more flow than a smooth straight pipe.

I really dont want custom headers but a turbonetics manifold..

I did some research compared to a turbo diesel convo.. I can turbo the 1FZ, add a sub tank, get a econo box honda for heavy rain days (ride cycle nice ones) and have money to spare..

A long tapered transition? Are you wanting to put a megaphone exhaust on a street vehicle? Maybe like a VW sand buggy or a motorcycle?

Wherever you start to widen your exhaust after the collector/secondary pipe is where you engine thinks the end of your tail pipe is for the purposes of scavenging. If you are at the track running 6-8k rpm (or higher) than a 10-12 inch secondary (or shorter if your on a bike) may be right on, but if you are on the street (with a car or truck) you are gonna want your exhaust tuned for lower rpms.


Edit: Exhaust after a turbo is a different animal since scavenging is replaced with powering forced induction. In that case, Pilargo Emilio.

[jamisobe]

Originally Posted by LC80Ducati996

Anyway what I am getting at is going from stock or near stock diameter from the collectors to the cats and using a long 7-12 degree conical transition to go up to the 3" will likely perform better than going to a 3" collector at the OEM Y or going with larger tri ys.. You will have more velocity where it does the most good and more flow farther down where gases have cooled off after the cat(s).

Maybe go 2.5" into the muffler and out at 3". I don't think there would be any gain though you probably wouldn't hurt performance since the exhaust pulse would see the muffler as the end of the secondary. It would counter the purpose of quieting the system without performance gain.

There would be a negative performance effect from starting 3" pipe at the 2.25 OEM collector.

[LC80Ducati996]

Originally Posted by jamisobe

There would be a negative performance effect from starting 3" pipe at the 2.25 OEM collector.

That is where the conical transition comes into play..

One example.. 2.25" to 2.5" cone between collector and 2.5" cat. Then a 2.5" to 3" cone between cat and 3" muffler..

Transitions

these are top notch SS and other mfgs and grades of steel exist..

Sometimes you need to change from one small diameter to another larger diameter when you do that use a 7 to 12 degree included angle transition for the best flow.


So yes good tri-ys are probably best. If not an option then step up dimeters slowly untill you get to the 3" cat back for much better performance than a 1/2" stair step that will have big turbulence

[jamisobe]

Originally Posted by LC80Ducati996

That is where the conical transition comes into play..

One example.. 2.25" to 2.5" cone between collector and 2.5" cat. Then a 2.5" to 3" cone between cat and 3" muffler..

Transitions

these are top notch SS and other mfgs and grades of steel exist..

Sometimes you need to change from one small diameter to another larger diameter when you do that use a 7 to 12 degree included angle transition for the best flow.


So yes good tri-ys are probably best. If not an option then step up dimeters slowly untill you get to the 3" cat back for much better performance than a 1/2" stair step that will have big turbulence

Wherever your transition begins from the secondary is where the exhaust pulse dissipates. If you want to take advantage of scavenging, use a short secondary for higher RPMs. The lower the RPMs the longer your secondary needs to be to maximize the scavenging effect.

Land Cruisers aren't motorcycles.

[LC80Ducati996]

The laws of physics about gas temperature and velocity do not change when an engine is mounted on two wheels vs four.

I was not even getting into header design originally since the question at hand was a 3" exhaust system.. Gradually increasing exhaust diameter is nothing radical at all infact a proven concept.
Regardless of where the pulses end on a full street exhaust vehicle there is still exhaust flowing in a pipe after this point. At this point the gasses have cooled and slowed bunch and in order to move the same lb/min of gases you need more diameter to do it because of the the lower velocity.

[jamisobe]

Originally Posted by LC80Ducati996

The laws of physics about gas temperature and velocity do not change when an engine is mounted on two wheels vs four.

I was not even getting into header design originally since the question at hand was a 3" exhaust system.. Gradually increasing exhaust diameter is nothing radical at all infact a proven concept.
Regardless of where the pulses end on a full street exhaust vehicle there is still exhaust flowing in a pipe after this point. At this point the gasses have cooled and slowed bunch and in order to move the same lb/min of gases you need more diameter to do it because of the the lower velocity.

Prove that gradually increasing exhaust diameter in street vehicles improves performance.

I just posted a write up that says to tune properly the secondary tube length (off of the same size collector) has to remain constant for a certain length depending on RPM and that after the secondary run tube diameter is not important as long as restriction is avoided.

You seem to be disregarding this and continue to claim that the less resistance the better no matter what. Please help me understand what you mean and post it up so I can see to what regard you are referring.

[jamisobe]

This is what I think (maybe I'm wrong). You like bikes alot and a typical performance exhaust for a bike looks like what you are describing. The only thing is bikes have rpms going up to 10,000 and beyond. To properly scavenge the exhaust on one of these engines you may not even need much of a secondary at all. In fact, you probably would not even use a tri-Y header system but a 4 into 1 with a short 2-3 inch secondary followed by a megaphone exhaust/muffler.

Am I on the right track or can you show me what I am missing?

[LC80Ducati996]

Hey look a megaphone off a tri-y headers collector..

http://performanceweldingheaders.com/img/triypro.jpg

Come to think of it are'nt they on all race headers..

Hmm maybe tapering a full exhaust system up as it goes back as close as you can get to on a street car..

[landtank]

Originally Posted by LC80Ducati996

Actually it could. for $682

Turbonetics Exhaust Manifold - Sport Compact Warehouse - Import Performance Specialist

Ohhh $606

Exh. Manifold, Toyota Landcruiser - Turbochargers.com

But overnight shiping would be spendy,

I had one of those and got rid of it. No way that design was going on my truck.

[jamisobe]

Originally Posted by LC80Ducati996

Hey look a megaphone off a tri-y headers collector..

http://performanceweldingheaders.com/img/triypro.jpg

Come to think of it are'nt they on all race headers..

Hmm maybe tapering a full exhaust system up as it goes back as close as you can get to on a street car..

Maybe you could be the first.

[alia176]

Originally Posted by jamisobe

With headers and a custom mandrel Y-collector.

Gas mileage ranges from 15 to 17 mpg with good pick up. It sounds neat though I initially had to deal with drone at highway speeds.


This is what I used for the drone:



These photos are in order from the
Downey headers to the Flowmaster 70 series muffler:

At normal throttle it sounds stock, but at WOT it sounds racey.

I'm scratching my head as to how are you guys managing to route a 3" over the chassis rail



Could I get a pic or two of this area further away? I know there isn't a whole lot of room under the 80 with a camera!

I've used Droanmasters on v8s but never on a I-6. Any sound clips?

edit: while you guys are fiddling with the exhaust systems, are you giving any thoughts to 'anti stealing' the cats that's been rampant these days?

[LC80Ducati996]

Originally Posted by landtank

I had one of those and got rid of it. No way that design was going on my truck.

What was not to your liking about that design.

I have friends who have had great sucess with turbonetics cast manifolds on four bangers...

FWIW I found a place that has them for around $400

I am looking at both a local shop to make a small batch of 3" mandrel bent systems. I also found an overseas MFG of a 3" HDJ80 system that 95% of which could be used on a FZJ.. The down pipe will need to be cut and spliced to mate with the OE collector on a NA rig.. For a turbo rig you will need to make a dump pipe to route the turbine outlet and wg dump into the down pipe..

[concretejungle]

Originally Posted by alia176

I'm scratching my head as to how are you guys managing to route a 3" over the chassis rail

Look above at my post. It is a 3" over the frame. You can see where the heat shield had to be trimmed to make it work. Also the exhaust guy said it was such a pain in his ass to do, he won't do it again. Those pics are from jfz80's rig, but he does have a supercharger.

[LC80Ducati996]

Originally Posted by jamisobe

This is what I think (maybe I'm wrong). You like bikes alot and a typical performance exhaust for a bike looks like what you are describing. The only thing is bikes have rpms going up to 10,000 and beyond. To properly scavenge the exhaust on one of these engines you may not even need much of a secondary at all. In fact, you probably would not even use a tri-Y header system but a 4 into 1 with a short 2-3 inch secondary followed by a megaphone exhaust/muffler.

Am I on the right track or can you show me what I am missing?

Oddly enough the Akrapovic full system I have on my Ducati goes from 2 to 1 and back to 2 again. Mostly an x-pipe collector type of thing...

With cars have you seen steped and tapered (better) primary headers.. stahl headers came up with many advances.. Anyway many studies have concluded that gradually increasing diameter as the exhaust travels has a positive effect on flow. Yes a 10ft long 7 degree included angle stick of exhaust pipe being mandrel bent to fit aint ever going to happen. I was just saying even if the front most part of the system is not as big as the cat back you will still get gains from using the larger cat back. Especially if care is taken to use a smooth gradual transistion up to that diameter.

[landtank]

Originally Posted by LC80Ducati996

What was not to your liking about that design.

I have friends who have had great sucess with turbonetics cast manifolds on four bangers...

FWIW I found a place that has them for around $400

I am looking at both a local shop to make a small batch of 3" mandrel bent systems. I also found an overseas MFG of a 3" HDJ80 system that 95% of which could be used on a FZJ.. The down pipe will need to be cut and spliced to mate with the OE collector on a NA rig.. For a turbo rig you will need to make a dump pipe to route the turbine outlet and wg dump into the down pipe..

the layout wasn't thought through for our trucks. My design places the turbo underneath the main runner just behind the engine mount similar to Safari. This greatly lessens the stress on the system when the engine torques, reduces under the hood temps, allows hangers to be attached to the head to support the manifold's weight, doesn't require re-routing the AC line or the water return line and should still allow for a York compressor. Mine will also have the EGR passage milled into it so it will not through a code. That passage needs be added to the turbonetics.

People have used that manifold but it's a real clumsy solution as far as I'm concerned.

[LC80Ducati996]

Its all about ETA and $ between your and their manifold..

An engine management solution will be required to tune it for the increase in induction.. I dont get smogged.. It will still run clean and not be big poluter but any aftermarket EMS will not have OBDII and the associated CELs.. Though many can be setup to run a EGR solenoid and setup properly there are some gains (minor) to be made MPG wise with a EGR system..

[jamisobe]